Cooperative Download in Vehicular Environments. Article (PDF Available) in IEEE Transactions on Mobile Computing 11(4) - · May with download rate of vehicular users in urban/suburban environments, and that such a result holds the major challenges of vehicular cooperative download in PDF of the aggregate download rate for a varying number of. Environment Perception Approach for Vehicular Ad hoc Networks. VTC . of cooperative safety applications and optimize the network.

In order to retransmit, the safety messages need to be buffered. Fair resource allocation is the critical metric where each node expects to get an equal amount of bandwidth and power consumption. VC 2 -MAC: The streaming task assignment method assigns streaming tasks to relay nodes, and the packet forwarding strategy defines the forwarding sequence of the stored video data in a relay node. Distributed relay selection strategy based on physical-layer fairness for amplify-and-forward relaying systems. Another version of precoded blocks is transmitted during the second level of broadcasting phase from previously used antennas.

These networks are formed among moving vehicles, road side units RSUs , and pedestrians that carry communication devices. Vehicular networks can be deployed in rural, urban, and highway environments. There are three main scenarios for vehicular communication: Some of the key technologies that shape the modern automobile industry and vehicular networks are described in [ 52 ] and [ 53 ] respectively. With the advancements in communication technologies, a number of promising applications are emerging for vehicular networks.

These are mainly related to infotainment, active road safety, and traffic management. These applications impose different service requirements in terms of latency, throughput, and reliability on the network. Cooperative communication is an emerging technology that is capable of enabling efficient spectrum use by exploiting the wireless broadcast advantage of overhearing the signal transmitted from a source to a destination.

Considering these features, cooperative communication technology can play an important role in improving the overall performance of vehicular networks.

Similar to other wireless networks, cooperative communication in vehicular networks has also been leveraged to offer various improvements; namely, spectral efficiency, increased transmission reliability, and reduced transmission delay [ 60 ], [ 61 ]. CVN enables neighboring vehicles to cooperate with each other by sharing information at different layers of the network so that it has multiple transmission alternatives for robust communication.

Vehicles can cooperate with each other either directly or through a roadside infrastructure. Usually, the vehicular node which helps the sender node to transmit its data is called a helper node or relay node. The relay node can operate in different transmission modes such as amplify-and-forward, decode-and-forward, compress-and-forward, and store-carry-and-forward.

A summary of various strategies for cooperative communication in vehicular networks is presented in [ 62 ].

Figure 2 shows a simple illustration of CVN where cooperation is performed in different ways. For example, a vehicle can provide assistance to other vehicles with failed direct transmissions, as illustrated in Figure 2a. Similarly, a vehicle can assist a RSU in relaying its packets to other vehicles, which are out of the RSU transmission range Figure 2b.

Figure 2c shows a scenario where both RSU and vehicle node, are involved in relaying failed packet transmission. For instance, when a source RSU fails to successfully transmit a packet to the targeted destination, it forwards the failed packet to the next RSU along the path using the backhaul wired connection. The new RSU relays the received packet to a vehicle, moving towards the targeted destination, that carries and transmits the relayed packet when it is in transmission range of the targeted destination.

Revenue Maximization, -: Not mentioned. In wireless networks, exploiting spatial diversity is one of the mechanisms for enhancing the reliability of a message by transmitting it through two or more different communication channels.

Spatial diversity is achieved by using multiple antennas of both transmitter and receiver. Conventional MIMO systems are an example of achieving the spatial diversity using multiple antennas [ 63 ].

In some cases, it is infeasible or costly to achieve spatial diversity by employing multiple antennas. In such scenarios, spatial diversity is achieved by enabling cooperation among multiple nodes to obtain similar benefits as achieved by conventional MIMO systems.

Such spatial diversity is called cooperative diversity. Figure 3 provides an illustration of cooperative diversity. The data transmission considered in the analysis is involved into two main phases: Each phase is further divided into two levels.

During first level of broadcasting phase, source node sends two precoded blocks from two different antennas. Another version of precoded blocks is transmitted during the second level of broadcasting phase from previously used antennas.

Similarly, the relaying phase is also divided into levels. In each level, the relay first amplifies the received signal and then transmits the resultant signal to the destination. To investigate the achievable diversity gain in these phases pairwise error probability expressions are derived.

The investigation reveals that the significant diversity gain is achieved through MIMO deployment and encoded transmission. In another work, Nguyen et al. These cooperative strategies rely on cooperative relay, multihop, and cooperative MIMO techniques.

The cooperative relay and cooperative MIMO techniques are more energy efficient than the multihop techniques. Further, for a given transmission distance, an optimal cooperative MIMO scheme selection is proposed to select the optimal antenna configurations.

Illustrations of cooperative diversity [ 64 ]. Similar to traditional wireless networks, the design of the MAC layer protocols in vehicular networks is also vital for improving network performance.

Generally, MAC layer protocols can be divided into three major categories: Contention-free MAC protocols rely on a scheduler to regulate participants by defining which nodes may use the channel and at what time. TDMA is a contention-free channel access mechanism that divides time into multiple slots. These time slots are assigned to vehicular nodes for communication. The number of time slots assigned to a node depends on the data volume. Here, we discuss the contention-free cooperative MAC protocols proposed for vehicular networks.

Cooperation is offered by a relay node only if the following conditions are satisfied: If there are multiple potential relay nodes, the one that first announces to relay the packet will become the relay, while the remaining nodes will not participate.

Bear in mind that cooperation is performed by a relay node during an unused time slot to relay the packet for which direct transmission failed. Therefore, the cooperation does not affect regular communication. The use of unused time slots for cooperative transmission by the relay ameliorates throughput the VANET. However, CAH-MAC is suitable for a scenario where the relative mobility is negligible; otherwise, the protocol faces slot reservation collision.

Even in the case of no collision, relay nodes consume available unreserved time slots for cooperative transmission, which lessens the opportunities of other nodes to find an unreserved time slot. They observed that reservation of a time slot leads to cooperation collisions that degrade network performance.

The relay node performs cooperative transmission if no possible communication is detected in its one-hop neighborhood and that of the destination. Although the proposed collision avoidance scheme in eCAH-MAC enhances unreserved slot utilization, switching between the sending and receiving mode on both nodes relay and destination is required within a time slot that intensifies system complexity.

The entire process of cooperation includes three key tasks; transmission failure identification, appropriate relay selection, and collision avoidance with other potential relays and packet retransmissions.

To offer a reliable broadcast service, CCB-MAC introduces an ACK message that cluster members destination nodes send back to the cluster head on successful reception of a broadcast message. If the ACK message is not received by the neighboring nodes of a destination, they will consider it an unsuccessful transmission for the destination, and themselves as potential relays. To avoid possible collision, the cluster head assigns a time slot to each potential relay node for transmission. When one relay transmits the failed packet to the destination node, other relay nodes suspend transmission of the packet after overhearing the transmission.

Although the proposed MAC enhances the successful reception rate of the safety messages, the exchange of ACK message against each broadcast message puts significant communication overhead on the CCB-MAC protocol and increases the interference. This causes huge overhead as a result of frequent cluster head selection.

Usually, VANET communication has to rely on multi-hop relays if the distance between the source and destination is larger than a one hop transmission range. However, selection of a relay node is critical because of the vehicles mobility. If the selected relay node has a longer buffer of packets ahead of the packet that needs to be relayed, then the destination may go out of the relay node transmission range, while waiting for transmission.

In this case, the authors suggested to use a neighbor of the relay node as a cooperative node to forward the packet if its own buffer is empty. When the relay node receives a packet from the cooperative neighbor, it deletes the packet from its buffer.

The cooperative node offers cooperation to a relay only considering its own empty buffer without considering channel conditions. Although contention-free MAC protocols provide deterministic delay, time synchronization is required for each participant. The time slots are reserved for the nodes and channel can be accessed without any contention. However, the scheme usually suffers from dynamic transmission delay in dense networks and topology changes.

Scalability, non-periodic data, and assigning time slots to nodes with diverse data rates are some of the others main concerns in implementing contention-free MAC protocols.

In the case of contention-based cooperative MAC protocols, a node has to contend with other neighboring nodes that are also interested in getting access to the channel for transmission. Carrier-sense multiple access CSMA is a contention-based mechanism that is used to access shared medium for transmission.

In the following, we discuss contention-based cooperative MAC protocols for vehicular networks. During the information exchange period, nodes that are within range reveal their existence to the other nodes, channel state and topology information that are required in the later stages of the protocol.

During relay-set selection, an optimal relay set is chosen among potential relay vehicular nodes. Finally, in the data forwarding period, the selected relay nodes broadcast packets received from the gateway. Although VC-MAC aims to maximize system throughput, the protocol faces higher channel access delay in non-uniform relay distribution scenarios and severe exposed node problem in a dense vehicular networks.

Figure 4 illustrates both the non-uniform relay distribution problem and the exposed node problem. In the non-uniform relay distribution, some of the destination nodes are far from the relay nodes. The required two-hop forwarding of data slows delivery of the necessary information. The exposed node problem causes extra delay in the transmission by the second relay. Illustration of the non-uniform relay distribution problem and the exposed node problem.

T R , T D , and T SD denote the information exchange time of relay, first level destination, and second level destination, respectively. The exposed node problem is resolved by letting the two relay nodes to exchange their neighbors information in a single cycle. After successful end of the handshake process, the sender starts transmitting the data.

This reduces complexity of network operation. However, the triangular handshake contributes additional delay in the actual transmission delay of the data. Mizar operation is comprised of three phases: The RSU disseminates an RTS packet along with the size of the packet to be transmitted and the concurrent data rate at maximum transmission power level.

After reception of data from the RSU, the optimal relay finds the concurrent data rate and determines the tolerable power for concurrent transmission. Although Mizar significantly increases the throughput and minimizes the transmission delay as compared to basic relay-based cooperation mechanism, the packet level cooperation may incur a significant overhead particularly in continuously varying channel conditions.

Mizar relay selection and power adjustment. Unlike contention-free cooperative MAC protocols, the absence of a schedule for transmission induces packet loss and variable latency due to randomness. Another drawback of contention-based cooperative MAC protocols is packet collision caused by hidden terminals and increased network density.

Like TDMA, hybrid MAC protocols experience less collisions among two-hop neighbors and attain high channel utilization under extreme contention conditions. The RP is comprised of several emergency slots used for collision-free safety message transmission, whereas CP is used for service slot selection or to reserve emergency slots of the RP. The CER-MAC enables nodes to use their own reserved time slots or time slots allowed by neighbors for transmission of safety messages.

Service channel resources are used for non-safety message transmissions during the control channel interval. In order to retransmit, the safety messages need to be buffered.

In case of high packet arrival rate, the number of safety messages stored in the buffer becomes higher. Also, there is a limit on number of safety messages that can be broadcasted in a sync interval. Therefore, some of the buffered safety messages cannot be re-broadcasted before time-out. Unlike achieving space diversity by employing multiple antennas on both transmitter and receiver to improve the wireless link quality, the space diversity can also be achieved by enabling the cooperation among nodes [ 76 ].

Such cooperation among nodes along the route can be enabled by designing and employing cooperative routing protocols. The cooperative routes are usually the concatenation of direct-transmission links and cooperative-transmission links [ 27 ]. The cooperative-transmission links are formed by utilizing the services of relay node for forwarding of the packet between transmitter-receiver pair. Similar to other wireless networks, there has been a growing interest in designing cooperative routing protocols for vehicular networks.

These routing protocols incorporate the available node diversity along the path while finding the route between a source and a destination. As we have discussed above, the routing protocols in CVN have a special requirement of finding the paths which can fully exploit the available forwarding relay options at each hop to enhance the transmission performance. To meet this requirement, researchers are investigating different methods of designing cross layer routing protocols that can share and use physical layer information.

The objective is to monitor and identify misbehaving vehicles. A cooperative watchdog model is employed to minimize the number of false alarms and ameliorate misbehavior detection probability.

The GEC routing protocol is comprised of numerous components that are involved in discovering cooperative paths and distributing the traffic over these paths. The GEC architecture has two key phases; route discovery and route maintenance.

However, the proposed solution has not incorporated the service differentiation that can be vital to consider for effectively fulfilling the requirements of various kind of traffic. A new approach to path selection is presented to optimize the trade-off between end-to-end reliability and transmission power consumption. Two optimization problems are formulated and investigated to meet the different requirements.

The second objective function is to minimize total power consumption subject to given constraints on end-to-end reliability. The optimized solutions for both functions provide criteria to find the best route among the available options. Though the proposed routing selection criteria find the efficient route in terms of transmission power and end-to-end reliability, the proposed solution assumes only one route in the network.

The co-channel interference caused by multiple active source destination pairs is not considered in the solution. Hence, performance of the protocol may degrade if the multiple routes in the network become active. A cross-layer routing protocol for VANET with the objective of maximizing the throughput and overwhelming the wireless channel unreliability is discussed in [ 16 ]. The route discovery and management are performed by the AODV-like protocol.

Then, a new relay selection algorithm is proposed with the objective of maximizing the throughput. The selection criteria cost uses estimated connection time and the physical layer information, such as SNR. The relay with the highest cost is selected among those available. When a relay node receives a frame from a sender, it decodes the frame.

If the frame is decoded successfully, the relay forwards the frame in its reserved slot. Otherwise, it discards the frame and remain silent during its reserved slot. To further improve the stability and reliability of the routing path, a MAC protocol is proposed to extend the route duration.

Though the proposed routing protocol maximizes the throughput, the research work assumes that every vehicle is directly associated with RSU. This requires a large number of RSUs, resulting into a high deployment cost. In cooperative routing, the main focus is on finding the paths between source and destination that can exploit the physical layer diversity.

However, cooperative forwarding involves in finding an alternate node on each individual hop for transmitting a packet. Herein, we discuss the research works, which consider the cooperativeness in forwarding mechanism. Cooperative positive orthogonal code POC -based forwarding mechanism for vehicular networks is discussed in [ 77 ].

POC-based forwarding exploits the wireless broadcast characteristic and spatial diversity by employing multiple forwarding nodes at each hop. To minimize the number of collisions, a set of relays is selected that uses a POC codeword to define the nodes transmission pattern. A set of cooperating relays that shares the POC codeword forms a virtual relay.

Each virtual relay node shares its transmission opportunities among its cooperating relay member nodes. Though the proposed solution improves the transmission success ratio, the channel condition has not been considered while forwarding the message. With the restriction of fixed number of messages transmitted within a frame, the node may send either too few or too many packets.

Too few packets may increase unreliability and too many packets may lead to significant overhead. One of the goals of implementing cooperativeness in forwarding is to minimize the number of retransmissions. This can be further improved if the forwarding mechanism employs network coding. Network coding is a well-established technique known for its capability to minimize the number of retransmissions [ 95 ]. A network coding-based cooperative forwarding mechanism is investigated by Celimuge et al.

The master node selects the forwarding slave nodes according to the direction, stability, and closeness to the master node. The source and forwarding nodes encode the packet using linear network coding with fixed coding vectors. In both reactive and proactive routing protocols, the slave address is inserted in the route reply message and periodic update messages, respectively. Therefore, the source node can find the master and slave forwarding nodes using any of the routing protocols.

Despite the proposed scheme significantly improves the packet delivery ratio, the network coding may introduce additional delay on each hop which can significantly increase end-to-end latency for each packet. Lee et al. Huang et al. The relay node is selected based on information such as hop-count distance, neighboring nodes and their hop-count distances, and available bandwidth. Video encoding and packetizing that is composed of multiple network abstract layer units is discussed in [ 97 ].

The streaming task assignment method assigns streaming tasks to relay nodes, and the packet forwarding strategy defines the forwarding sequence of the stored video data in a relay node. The base layer of the streaming video is downloaded by the requester, whereas the enhancement layers are transmitted through relays and forwarders.

The proposed protocol can adapt to the dynamic characteristics of the network and smoothly transmit video hop by hop. The CSCF scheme considers bi-directional vehicular traffic flow and chooses two relay vehicles in both directions. The relay selection criteria takes into consideration transmission outage time while moving between two RSUs. Initially, the data is forwarded to the first relay by the first RSU.

Then, the data is forwarded to the second relay by the second RSU. The relay vehicle node stores the data and then transmit it as soon as a communication link with the target vehicle is established. Evaluation of the proposed solution demonstrates that the CSC-based transmission scheme minimizes transmission outage time. Liu et al. RSUs can share the data to passing vehicles using a V2I communication channel, whereas vehicles can also deliver cached data to their neighbors using a V2V communication channel.

The proposed solution works in three phases. During the first phase, each vehicle advertises its presence and collects information about neighboring nodes by exchanging and receiving heartbeat messages. During the third phase, each vehicle changes its operational mode according to the scheduling decision made by the RSU.

Further, a cache strategy is proposed to maximize the network coding impact. Although the proposed network coding-assisted data dissemination improves the service performance, the network coding may induce additional delay on each hop, thereby increasing end-to-end latency for each packet. Mehar et al. The DHVN selects a farthest away node in each direction as a relay node to enable fast dissemination of data.

Furthermore, DHVN has the capability to adapt itself according to road architecture and vehicular environment. The proposed protocol utilizes an algorithm that optimizes packet retransmission, especially at intersections. Further, a store and forward mechanism is added to mitigate the effect of disconnections in a partitioned vehicular network.

DHVN offers a high delivery ratio, low end-to-end delay, and minimum bandwidth. Bharati and Zhuang [ 83 ] propose a cooperative relay broadcasting CRB scheme to rebroadcast neighboring source node packets to increase the reliability of broadcast transmission. Furthermore, an optimization framework and a channel prediction scheme based on a two-state Markov chain is proposed. The optimization framework gives an upper bound on the performance of CRB, whereas the channel prediction scheme helps in choosing the best relay node.

CRB also supports proactive cooperation decisions that helps in delivering the packets before they expire. Unlike cooperative forwarding schemes that exchange a huge amount of information to coordinate, Zhang et al. The use of location information enables the node to take forwarding decision without any prior coordination with its neighbors. Though the proposed scheme reduces the coordination overhead, the location-based forwarding rely on global positioning system information that may not be available in tunnels.

Cooperative link scheduling is the process of selecting a subset of links such that the nodes can concurrently utilize the cooperative links while transmitting simultaneously without interfering with the receptions of each other. Figure 8 illustrates the concurrent scheduled link in vehicular networks where links corresponding to same color edges can be active simultaneously.

Link scheduling and resource allocation as a joint optimization problem is proposed by Zheng et al.

They present a two-dimensional-multi-choice knapsack problem 2D-MCKP -based scheduling scheme for 2-hop vehicular networks. The scheduling scheme selects coordinator vehicles for each sink vehicle and also assigns radio resources to V2V and V2I links to address the maximum sum utility optimization problem. The proposed scheduling scheme enhances the average utility with justifiable computational complexity.

However, the scheme does not consider the requirements of multiple services and dynamic process of data packets arrival.

Pan et al. A cooperative communication-aware link scheduling is proposed to address the problem. The network is modelled in the form of a graph where normal links are extended by introducing a dummy cooperative relay node. This is to make sure that the direct link communication representation is compatible with that of the relay-based cooperative communication.

In the graph, each vertex is considered as a resource point for scheduling and represented by an extended link channel pair. Then a 3-D cooperative conflict graph is established to represent interference among cooperative extended links. From the conflict graph, independent sets and conflict cliques are defined to demonstrate which extended links can be active simultaneously and which cannot. Using a 3-D cooperative conflict graph, the problem is formulated as a throughput maximization problem subject to various constraints i.

The problem is near-optimally solved by linear programming and provides feasible results using a simple heuristic algorithm. Zheng et al. The scheme consists of three phases: The vertices in the weighted bipartite graph represent the vehicles.

These vertices are divided into two groups: The weights on the edges are based on the capacity of the communication links between vehicles.

Next, a maximum weighted matching problem of bipartite graph is solved by the Kuhn—Munkres algorithm. Finally, in the third phase, a search algorithm is employed to determine the optimal separation. The bipartite graph-based link scheduling algorithm has lower complexity than the exhaustive search, hence providing better fairness. However, the proposed scheduling scheme does not incorporate the user arrival and departure process that is critical factor in vehicular environment.

Zhang et al. The energy efficiency in cognitive vehicular networks is formulated as an optimization problem, which is solved by using the recursion method. Based on an optimization model, a cooperation relay scheduling scheme is proposed that aims at enhancing the performance of the network in terms of energy consumption.

The relay selection is based on the distance of the candidate node from the source node. The proposed relay scheduling scheme improves the network performance in terms of energy consumption. There have been a number of interesting studies that aim at investigating the impact of various cooperative strategies on the performance of vehicular networks. In the following, we present research efforts that are mainly concerned with analytical models in the context of cooperativeness in vehicular networks.

For instance, V2V and V2I communications and the effect of node mobility to optimize the throughput performance has been investigated by Chen et al.

The authors propose a strategy that enables the vehicle of interest VoI to receive data from an infrastructure e. When the VoI leaves the transmission range of infrastructure, it relies on V2V communications to continue reception of the data via relay nodes. Moreover, an analytical framework is proposed for investigating the data transmission process under cooperative communication strategies. Shirkhani et al. The proposed scheme relies on the location of relay nodes without incorporating channel state information.

A closed-form expression is derived for the symbol error rate. The effect of rate and transmission range on cooperative vehicle safety systems is examined by Fallah et al. Based on their investigations, a model is proposed that quantifies the performance of a network using a channel busy ratio as feedback.

Initially, a node behavior is modeled, then the effect of a hidden node on channel busy time ratio and collision probability is investigated. An analysis of the joint effect of three key elements of CVN: To conduct the analysis, a Nakagami fading channel model is considered with independent and identically distributed i. A closed-form expression of the connectivity probability is derived and a lower bound on the cooperative ratio is determined.

The connectivity probability for both i. Feteiha et al. Closed-form error rates expression is derived for the analysis. Numerical analysis shows that a significant coverage improvement is achieved by extending transmission distance with the same transmitting power.

Nguyen et al. The performance of these cooperative techniques is compared with that of a traditional multihop technique. The relay techniques outperform the single-input-single-output SISO techniques, but are less efficient than the cooperative multiple-input-single-output MISO techniques in terms of energy consumption.

The relay techniques also out-perform cooperative MISO in the case of high transmission synchronization error that results in better energy efficiency. Chen et al. An analytical framework is designed to investigate the data dissemination process under proposed cooperative communication strategy.

A close-form expressions are also determined for achievable throughput that shows the relationship between key performance-impacting parameters e. Here, we discuss those research works that consider cooperativeness while allocating power and resources.

Xiao et al. The proposed solution takes advantage of the ranking value computed for channel characteristics at relay nodes. Further, the relaying method optimizes transmission power to minimize outage probability and relay nodes can change modulation levels to enhance spectral efficiency. Ilhan et al. The communication channels are modeled as cascaded Nakagami fading. A diversity order for these scenarios is obtained by deriving the pairwise error probability. Then, a power-allocation problem is formulated to find the share of the transmit power between the relaying and broadcasting phases for optimization of performance.

Real-time video streaming for vehicular networks is studied by Yaacoub et al. The authors propose a cluster-based cooperative communication technique for real-time video streaming where moving vehicles are grouped into cooperative clusters. Error concealment techniques, along with efficient resource allocation mechanisms are used to improve the quality of the received video. The proposed methods have significantly improved Quality of Experience QoE and Quality of Service QoS compared to the non-cooperative vehicular networking scenarios.

Group communication is a critical concern when the objective is common among vehicles. Herein, we discuss the research works, which consider cooperativeness in group communication scenarios.

The simulation results demonstrate that the proposed solution asymptotically meets the SSGC constraint when the transmission power is correctly assigned. Saad et al. The problem of revenue optimization is formulated as a coalition game among RSUs.

In a coalition game, multiple players form a group to participate in a game instead of participating individually. Then, a distributed algorithm for coalition formation is proposed that enables RSUs to distributively join and leave a coalition while optimizing their utility.

The utility considers the gain from cooperation and cost incurred on coordination. Simulation results demonstrate that the proposed algorithm enables RSUs to self-organize while enhancing the payoff between Similar to other wireless networks, security is also an important issue in vehicular networks.

Luo and Liu [ 99 ] have highlighted a number of threats and solutions for wireless telematics systems in intelligent and connected vehicles. The security concerns may further be intensified when a vehicular network allows the cooperation among the nodes because of the likelihood of malicious behavior in cooperating nodes.

Cooperative Vehicular Networking: A Survey

Zhu et al. Both parameters performance is optimized using cooperative communication. Also, a prevention-based security scheme is proposed that offers both hop-by-hop and end-to-end integrity protection and authentication.

An outage capacity, bit error rate and a closed-form effective secure throughput are derived by incorporating both security and QoS provisioning in VANETs. The proposed scheme has significantly enhanced secure throughput of VANETs by exploiting cooperative communications. Lai et al. SIRC motivates the vehicle users to support each other in securely downloading-and-forwarding packets.

The proposed scheme is comprised of two phases: Further, a reputation system is implemented to motivate cooperation and penalize the malicious vehicles. An enhanced SIRC is proposed that utilizes reputation system to encourage the packet forwarding and achieve reliability.

During the cooperative forwarding phase, an aggregating Camenisch-Lysyanskaya CL signature is utilized to ensure security of the proposed incentive mechanism.

Cooperative Vehicular Networking: A Survey

A vehicle and infrastructure centric metrics have been proposed to accurately measure the vehicle safety awareness. The vehicle nodes employ the vehicle heading based filtration mechanism to incorporate the critical neighbors for awareness calculation.

The vehicle heading based filtration mechanism finds critical vehicles, which are potential accident threat, among the neighborhood. The infrastructure nodes also incorporate the position error of each neighbor vehicle while calculating the awareness. The metrics are comprised of a number of received cooperative awareness messages CAMs , their safety importance, accuracy, and vehicle heading.

The authors claim that the proposed metrics outperform other contemporary metrics used in measuring VANETs safety awareness.

Figure 9 shows the thematic taxonomy of cooperative vehicular networks. The existing literature is categorized based on the following characteristics: This category of research work refers to the main goal of integrating cooperativeness in CVN.

Current research efforts in cooperative vehicular networking aim to attain a number of objectives, such as throughput maximization, power allocation optimization, transmission outage minimization, reliability improvement, utilization maximization, and reservation slot collision minimization.

Similar to other wireless networks, exploiting available resources to maximize the overall network throughput is the primary challenge in CVN. Throughput maximization in CVN has been studied in various ways, such as designing a cooperative MAC [ 11 ]—[ 13 ], [ 69 ], [ 73 ], [ 85 ], cooperative routing [ 16 ], and cooperative link scheduling [ 19 ]. The optimization of transmission power allocation is another objective targeted by some of the research works [ 15 ], [ 86 ].

For instance, the main focus of the work presented in [ 15 ] is to minimize transmission power consumption while considering the constraints of reliability and performance, whereas the works proposed in [ 86 ] optimize the power allocation to relaying and broadcasting phases.

Transmission outage time minimization-based approaches aim to reduce the no-coverage period between vehicles or V2I during the transmission session.

The transmission outage can be along highways where the RSUs are deployed sparsely and intermittent connectivity is available. In the case of larger uncovered areas, transmission outage can be intolerable to delay-sensitive applications.

To minimize the impact of transmission outage on delay-sensitive applications, Wang et al. The SCF scheme enables a vehicle in the transmission coverage area to store the received data, carry, and forward it to the targeted vehicle in an uncovered area. Transmission reliability refers to a percentage of correctly transmitted packets between the nodes in a vehicular network.

Efficient resource utilization is an important objective for network operators to obtain a good return on their investments.

The protocol presented in [ 71 ] aims to maximize the utilization of an unreserved time slot. The work reported in [ 20 ] maximizes sum utility of vehicular networks by incorporating a two-dimensional multi-choice knapsack problem- based scheduling in cooperative vehicular networks. In order to cooperatively transmit failed packets of neighboring nodes, the relay nodes have to reserve time slots to transmit failed packets. Cooperative transmission can be performed only if the destination vehicle node does not notice the attempt to reserve the slot from another relay among its 1-hop neighbors.

C-ACK is introduced by Bharati et al. By minimizing the reservation slot collision, the throughput of the network can be increased. The cooperative transmission mode defines the necessary set of actions performed by the cooperating nodes for a particular cooperative transmission. These transmission modes can be divided into four classes, namely, amplify-and-forward, decode-and-forward, compressed-and-forward, and store-carry-and-forward. The amplify-and-forward transmission mode enables the relay node to amplify the received signal before forwarding it to the destination node.

The decode-and-forward transmission mode enables the relay node to decode the overheard transmission and forward it after correctly decoding the packets. In the case of unrecoverable errors, the relay node will not be able to participate in the cooperative transmission. The compress-and-forward transmission mode enables the relay node to compress the received signal before forwarding it to the destination. The store-carry-and-forward transmission mode enables the relay node to store the received packet temporarily and carry it until the relay node reaches into coverage of the destination node to forward it.

Cooperation-based network functions refer to networking related functions that implement cooperativeness to optimize the performance of a vehicular network.

The key functions, which implement cooperativeness, are routing, MAC, and link scheduling. Cooperative routing involves in finding the routes between source and destination which can exploit the available forwarding relay options at each hop to improve the transmission performance. Cooperative routing enables multiple relays at each hop to cooperate either at the symbol-level or packet-level to forward the message. Cooperative routing reduces the number of times a route has to be rediscovered, thereby minimizing the network overhead and delay.

Cooperative MAC protocols leverage medium access contextual information and available resources to improve link-level data reliability. Cooperative link scheduling refers to the problem of coordinating interfering links among cooperating nodes so that network performance can be optimized. Most cooperative link scheduling research work is aimed at maximizing the throughput and enhancing the average utility of the network.

Cooperative device types refer to the type of nodes in the vehicular network which assist other vehicular nodes in making their transmission successful.

Usually, relaying vehicles, non-relaying vehicles, and RSUs are the cooperating devices in a vehicular network. The relaying vehicles cooperate with the sender node by re-transmitting failed packets to the destination in an available time slot. Non-relaying vehicles cooperate with the relay nodes by transmitting a packet of the relay node for which they can minimize the delay.

An RSU cooperates with other RSUs by transmitting their overheard packets in the available time slots that have failed; thereby minimizing the transmission overhead. The main communication technologies that are used in cooperative vehicular networks are IEEE IEEE The standards main objective is to support wireless access in vehicular environments.

It defines the amendments to IEEE The peak download and upload data rates supported by LTE are up to With the support of a wide range of cell radii from 10 km to km, the standard is suitable for vehicular networks [ 51 ].

Vinel investigates the suitability of IEEE To meet the requirements of emerging delay sensitive applications, researchers are investigating the fifth generation 5G mobile communication systems to integrate it into the future vehicular networks. Though the standard is not fully defined yet, 5G systems will possess a number of characteristics that assist in realizing the vision of several intelligent transport systems application. These characteristics are a large number of antenna arrays, high bandwidth, network densification, use of millimeter wave mmWave , and direct device-to-device communication.

With these unique characteristics, the performance of several applications including vehicle navigation and critical safety applications can be significantly improved. Considering the capabilities of 5G, researchers in the domain of vehicular networking are taking initiatives to exploit the technology for improving the performance of vehicular applications.

Dong et al. Wymeersch et al. Va et al. In their another work [ ], the authors proposed an optimal design of mmWave beam to maximize the data rate for V2I communication.

Tassi et al. Figure 10 illustrates the mm-wave-based cooperative communication in vehicular networks. Illustration of a scenario for mmWave-based Cooperative communication in vehicular networks. The standard aims at offering a data rate of up to 7 Gbps. Kumari et al. CVN possesses the unique characteristic of enabling cooperation among vehicular nodes. The unique feature imposes several new requirements on vehicular networks that should be fulfilled to realize the vision of CVN. Herein, we are discussing some of the key requirements.

The quality of V2V and V2I communication links varies with space and time [ ]. Further, the speed of moving vehicles also intensifies the issue. Therefore, there is a need to design adaptive transmission power control protocols for cooperative vehicular networks. Existing static transmission protocols are not effective for dynamic run-time varying conditions caused by cooperation among moving vehicles.

Further, the adaptive transmission protocol needs a learning mechanism to become aware of the changes in surrounding vehicular environments, especially because of the cooperation among vehicles. Chunk Scheduling 2.

The Global chunk scheduling assumes that APs maintain per vehicle distributed chunk databases. The Local chunk scheduling is similar to the Hybrid scheme. To that end.

Since a same chunk can be transferred by one or multiple APs to one or more carriers. The Density-based AP deployment technique aims at maximizing the probability of direct data transfers from APs to downloader vehicles.

Under the Random AP positioning scheme. This technique exploits the predictability of large-scale urban vehicular traffic flows. The resulting placement may be considered representative of a completely unplanned infrastructure. Cooperative Download in Vehicular Environments Uploaded by ieeexploreprojects. Flag for inappropriate content.